Expandable hydraulic tappet with a variable exit valve

Claim 1

A pressure controlled expandable hydraulic tappet for use in an internal combustion engine to selectively vary the effective profile of a camshaft by extending the drive train between said camshaft and a camshaft operated mechanism, said tappet comprising: a housing having an internal piston receiving means; expandable piston means reciprocally disposed within said housing, said piston means defining a load cell chamber having an inlet port and an exit port; a supply of hydraulic fluid connected to said inlet port; inlet valve means interposed said fluid supply and said chamber and biased to assume a closed position, said valve means opening to admit hydraulic fluid into said chamber expanding said piston means when a predetermined valve opening force is exerted on the upstream side of said valve means and said inlet valve means resuming a closed position and entrapping said fluid within said chamber when the valve closing force downstream of said valve means exceeds said valve opening force; exit valve means connected to said exit port for selectively sealing or opening said chamber, said exit valve opening to effect exiting of hydraulic fluid from said chamber at a predetermined rate when pressure within said chamber exceeds said predetermined amount, said exit valve means having flow throttling means within said tappet for controling the rate of closing of said exit valve and for controlling the flow rate at which fluid exits through said exit valve means, said exit valve means including an exit ball, a mating seat to accommodate in sealing relation said exit ball, and an exit valve counter-bore extending downstream from said seat, said exit valve counter-bore having a diameter slightly greater than the diameter of said exit ball, said exit ball being disposed for reciprocal movement substantially within said counter-bore and defining in combination with said counter-bore an annular passageway that limits the fluid flow rate therethrough; and bias means for closing said exit valve and sealing hydraulic fluid within said chamber when the pressure within said chamber is below a predetermined amount.